AND CONCLUSIONS 1. The responses of neurons in the posteroventral (PVCN) and dorsal (DCN) cochlear nucleus of the unanesthetized cat were determined for both long and short tones. These results were compared with recent studies (13, 14) in the barbiturate-anesthetized cat conducted in the same laboratory using similar stimuli and analysis programs. 2. Every response pattern (poststimulus time histogram to short tones), which has been observed in previous studies using anesthetized animals, was

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... lso observed without anesthetic. The converse was also true: no novel response patterns were observed in the unanesthetized cat. This was also true for interval histogram, response area, isorate curve, and frequency sweep data. 3. Some neurons were difficult to classify into existing descriptions of cochlear nucleus response patterns. For example: I) primarylike, onset, pauser, and buildup response patterns could also show chopper-like properties; 2) onset-inhibitory, pauser, and buildup neurons appeared to form a response continuum rather than exist as separate response categories; and 3) onset neurons with low characteristic frequencies (CFs) often showed sustained and strongly phase-locked responses below -1,000 Hz. In addition, single neurons often showed more than one response pattern depending on the intensity and frequency of the acoustic stimulus. These ambiguities were also observed under anesthetic ( 13, 14) . 4. Onset neurons within the PVCN appear to be well suited for the encoding of temporal and intensity information. At low stimulus frequencies they often respond to every cycle of a pure tone stimulus and exhibit the highest degree of phase-locking in the cochlear nucleus. The dynamic ranges associated with many onset neurons can exceed 80 dB compared with the 30-to 40-dB dynamic ranges associated with most other cochlear nucleus neurons. Onset neurons show a similar range of activities in the anesthetized cat (13, 14) . 5. Neurons in the DCN have response properties that are more complex than those seen in the PVCN. Response patterns can change from sustained excitation to complete inhibition and are more often nonmonotonic near CF. DCN neurons can show well-defined tuning in the frequency domain and may be used to encode spectral information, but appear to be poorly suited for encoding temporal or intensity information as they are weakly phase-locked and have relatively small dynamic ranges. When DCN neurons "chop" they usually do so more slowly than do PVCN neurons. DCN neurons recorded in the anesthetized cat behave similarly ( 13, 14). 6. The relative frequency of a particular response pattern did vary with anesthetic state. The largest differences were observed for the DCN where onset-inhibitory neurons were nearly five times more common and chopper neurons were about half as frequent without anesthetic. The proportions of other neuron types in the DCN and PVCN differed by smaller margins. 7. Nonmonotonic rate curves were twice as common without anesthetic in the DCN. They were observed for 42% of the DCN neurons studied in the unanesthetized cat compared with 20% for the anesthetized cat. 8. Response properties were characterized parametrically for each resonse category in both the anesthetized and the unanesthetized cat. Parametric differences depended on the 414 0022-3077187 $1.50 Copyright 0 1987 The American Physiological Society UNANESTHETIZED CAT COCHLEAR NUCLEUS CELLS 415 location of the neuron but there were some general trends. Threshold, spontaneous rate, and the standard deviations of the first-spike latency and the interspike interval tended to have larger values without anesthetic. Differences in these parameters may have resulted from increased noise levels in the unanesthetized preparation. The dynamic range, the maximum discharge rate, the first spike latency, tuning sharpness (Qlo), the mean interspike interval, and the peak-to-steady-state ratio showed less consistent differences with anesthetic state. 9. These results suggest that it is still useful to study cochlear nucleus responses in the barbiturate-anesthetized cat, but that some caution must be exercised when one evaluates parametric data obtained under anesthetic.